A binaural rendering technology is essentially required to provide immersive and interactive audio in a head mounted display (HMD) device. Binaural rendering represents modeling a 3D audio, which provides a sound that gives a sense of presence in a three-dimensional space, into a signal to be delivered to the ears of a human being. A listener may experience a sense of three-dimensionality from a binaural rendered 2-channel audio output signal through a headphone, an earphone, or the like. A specific principle of the binaural rendering is described as follows. A human being listens to a sound through both ears, and recognizes the position and the direction of a sound source from the sound. Therefore, if a 3D audio can be modeled into audio signals to be delivered to both ears of a human being, the three-dimensionality of 2D audio can be reproduced through a 2-channel audio output without a large number of speakers.
Here, when the number of channels or objects included in an audio signal to be binaural rendered increases, the amount of calculation and power consumption required for binaural rendering may be increased. Therefore, a technology for efficiently performing binaural rendering on an input audio signal is required in a mobile device limited in calculation amount and power consumption.
Furthermore, when an audio signal processing device binaural renders an input audio signal using a binaural transfer function such as a head related transfer function (HRTF), a change of timbre due to characteristics of the binaural transfer function may cause degradation of sound quality of high-quality content such as music. When the timbre of content, from which high sound quality is required, changes significantly, a virtual reality effect provided to a listener may deteriorate. Therefore, a binaural rendering-related technology, which considers a timbre preservation and a sound localization of an input audio signal is required.